1. Field of the Invention
The present invention relates to a multiconductor cable incorporating a plurality of insulated wires, coaxial conductors, or the like and a method of producing the multiconductor cable, particularly to a multiconductor cable in which a plurality of wires and conductors are tied together in a bundle at the intermediate portion and are arranged in a flat array at both ends, where the cable is provided with connectors or similar components, and a method of producing the multiconductor cable.
2. Description of the Background Art
As information communications devices, such as notebook-size computers, cellular mobile phones, and video cameras, have been widely used in recent years, they are required to reduce their size and weight. Consequently, connection between the main body of a device and a liquid crystal display and wiring in a device are made using extremely fine insulated wires and shielded wires including coaxial conductors. In addition, a multiconductor cable in which the foregoing wires and conductors are bound together is also used because it facilitates the wiring. A multiconductor cable is electrically connected through a connector having the shape of a card-edge connector in which a multitude of contacts are arranged in a row (such a connector is used for the connection of a printed circuit, for example).
FIG. 6A is a plan view of an example of the conventional multiconductor cable, and FIG. 6B is a plan view of another example of the conventional multiconductor cable. In many cases, a multiconductor cable 1a provided with connectors as shown in FIG. 6A is used, in which a plurality of electric wires 2 are arranged in parallel with a constant pitch to form a unified structure as a multiconductor cable. The cable 1a is suitable for the wiring along the inside wall of a device. However, when it is used for the wiring through a hinged portion, such as the connection between the main body and a liquid crystal display of a cellular mobile phone, its twisting property is insufficient at the hinged portion. In particular, when the size of the hinged portion is small, the stress applied to the cable 1a is large and, consequently, the cable tends to suffer a break. Therefore, this type of cable is not suitable for use at a small-hinged portion.
To solve this problem, the wiring through a turning portion, such as a hinged portion for an opening-and-closing operation, is made using a multi-conductor cable 1b provided with connectors as shown in FIG. 6B. In this cable, both ends to which electrical connectors 3 are connected have a structure in which a plurality of wires 2 are arranged in a flat array and the intermediate portion has a structure in which the wires 2 are bundled together. In this case, the cable 1b may be produced such that only both ends have a flat shape and the intermediate portion is formed by bundling the intermediate portions of a plurality of disorganized wires. The cable 1b may also be produced by rolling up the intermediate portion of a plurality of wires that arranged in a flat array throughout the length. A plurality of wires 2 are bundled using a bundling member 4 having the shape of a tape. When the wires 2 are coaxial conductors or shielded wires, an intermediate portion of the multiconductor cable is sometimes provided with a grounding member 5 for connecting that portion to the ground.
In the multiconductor cable 1b composed of a plurality of wires 2 having the same length, wires placed in the middle position of a flat array are slackened and wires placed at the outside positions are pulled. As a result, the wires placed at the outside positions tend to break. To overcome this problem, the published Japanese patent applications Tokukoushou 61-230208 and Tokukai 2000-294045 have disclosed a multiconductor cable having a specific structure (see FIG. 4 of Tokukai 2000-294045). In this structure, a wire placed at an outer position has a length longer than that of a wire placed at an inner position so that the slack and tension can be prevented.
However, no disclosure has been made about the length of a wire placed at an outer position. No clarification is made for the case that undergoes twisting. In practical application, when a multiconductor cable provided with connectors has a length of E and a width of D and the length E is at least six times the width D, it is confirmed that the intermediate portions of the wires constituting the multiconductor cable and having the shape shown in FIG. 6A can be simply bundled to obtain the shape shown in FIG. 6B without any problem in use.
However, if the length E is small to the extent that the ratio E/D is less than six, a problem is caused due to the difference in length between the minimum length of the wire placed at the center of the bundle and the maximum length of the wire placed at the outermost position of the bundle. More specifically, at the time of bundling a plurality of wires arranged in a flat array, even when the length of wires to be placed at the outer side and to undergo tension is simply increased, a wire having an excess length tends to buckle or break. In addition, for the use in a turning portion, if no consideration is given to the twisting, a break of wire cannot be prevented, that is, the problem cannot be totally solved.